Thermo Time Switch Circuit

[rogerh113]

Hello,

I am having a bit of a sluggish start, and think it is likely the thermo time switch (happened before, and will probably happen again).  I was wondering if there is anything else in that electrical circuit I shold check that could be causing premature death for the switch.  The old one has lasted a pretty long time, but they are fairly expensive so I would like to get as much life as possible out of the new one.   Just thought I would inquire.

Thanks -- Roger

[ctaylor738]

I went through this on a 250SL, and posted on this thread. 

http://www.sl113.org/forums/index.php?topic=16747.0

Your problem may be similar, not enough voltage to open the valve at cranking.  Also, if your starter is tired, it can't turn the engine and thus the injection pump very fast, which means a less-than-optimal amount of fuel is getting the cylinders when cranking.

[rogerh113]

Thanks for the link - hope to start troubleshooting this week.  Clothes washer went down last week, and for some reason my wife prioritized that above my 113 !!!

I did measure the voltage at the manifold injector during cranking (cold), and it looked to be 6 to 7 volts.  First thing I'll do is detach the lead there and see what voltage is coming down the lead.  May tell me which direction to go (manifold or tricky electronics......)

Regards -- Roger

[ctaylor738]

Clean clothes are a good thing. 

That voltage is probably not enough to fire the valve.  I'm sure you will find the drop if you follow the circuit from the big lug on the starter.  The electronics are not very complicated once you understand how the relay works.

[ja17]

Hello,

During cold starts on your engine, the cold start solenoid on the injection pump should activate  and the cold start valve (CSV)  on the intake should activate. Check both of these devices with a 12 volt test light during cold start cranking first. Let us know if both seem to get any voltage at all.

[rogerh113]

Hi,

I'm reading about the same voltage on the lugs of the cold start solenoid on the injection pump - 6 to 7 volts.  I have not yet disconnected the leads to see if the voltage is up to 12 without the load.

Regards -- Roger

[garymand]

Roger, the voltage is too low.  It indicates high resistance from the terminals back to the battery.  To see what I mean, use a jumper wire from the battery to the cold start solinnoid terminal and measure the voltage at the terminal.  It will be nearly the same as the battery.  Don't bother to measure the voltage with no load.  With no load the voltage wiill be the same as the battery.  Look for a loose/corroded connection or relay contacts that are bad shape.  Your meter will measure the same voltage on both sides of a good connection, but lower voltage on the output of a bad connection.  With no resistance the voltage drop is zero.  The higher the resistanc, the higher the voltage difference.  You are loosing 6 volts somewhere.

[rogerh113]

I agree.  Time to pull out the blue book and work my way methodically through the circuit. 

Regards -- Roger